reduce allocations (also pulls in updated ironwood to do the same)

src/core/pool.go

@@ -0,0 +1,17 @@
+package core
+
+import "sync"
+
+var bytePool = sync.Pool{New: func() interface{} { return []byte(nil) }}
+
+func allocBytes(size int) []byte {
+	bs := bytePool.Get().([]byte)
+	if cap(bs) < size {
+		bs = make([]byte, size)
+	}
+	return bs[:size]
+}
+
+func freeBytes(bs []byte) {
+	bytePool.Put(bs[:0])
+}